This invention relates to an acidic shampoo composition. More particularly this invention relates to an acidic shampoo composition having improved cleaning.
Acid side shampoos, i.e. shampoos with a pH of less than seven have been known and in fact there are a number of shampoos currently on the market having a pH within the range of 5 to 7. It is known that high alkaline shampoos tend to damage hair and accordingly there has been a recent switch towards shampoo compositions which are less alkaline.
U.S. Pat. Nos. 2,289,004, 2,303,932, 2,599,665 and 2,892,756 describe acid side shampoo hair treating compositions. These patents describe compositions having pHs with the range of from 2 to 7 and indicate that damage to the hair can be minimized by using a shampoo having a pH near the isoelectric point of hair, i.e. pH 4.5.
Also there are a number of patents and publications which describe the use of anionic detergents as the cleaning agent in the shampoo composition. The most commonly used anionic detergent is sodium lauryl sulfate. This detergent is an effective cleaner for the hair and has reasonable solubility.
It has been found that an improved cleaning shampoo composition can be prepared by incorporating 12.5 to 25% by weight of an anionic detergent selected from the group consisting of M-lauryl sulfate, mixtures of M-lauryl sulfate and M-lauryl sulfate plus from 1 to 10 moles of ethyleneoxide and mixtures of M-lauryl sulfate and triethanolamine lauryl sulfate wherein M is selected from sodium, potassium and ammonium, from 1.0 to 3.5% by weight of an inorganic salt soluble in the composition and from 0.25 to 1% by weight of an acid selected from citric acid, boric acid, hydrochloric acid, phosphoric acid, ascorbic acid and mixtures thereof, the composition having a pH within the range of 3 to 4.5 and a viscosity within the range of from 4000 to 15,000 centipoise.
It is surprisingly found that the composition having an increased viscosity performs significantly better than a similar composition having a lower viscosity and that compositions having lower pHs perform better than compositions having higher pHs, furthermore the compositions having lower pH and higher viscosity perform better than the similar compositions having either higher pH or lower viscosity. The improvement in performance appears to be synergistic since the combined effects of increased viscosity and descreased pH are exceeded by the composition having increased viscosity and decreased pH.